The present invention relates generally to semiconductor processing. More particularly, the present invention relates to a method for determining the endpoint of a process performed within a processing chamber.
In the field of integrated circuit and flat panel display fabrication, multiple deposition and etching processes are performed in sequence on a substrate within one or more processing chambers to form various design structures. Processes such as physical vapor deposition (PVD), chemical vapor deposition (CVD), etching, etc., are well known in the industry and each result in residue build up in the processing chamber. For example, during CVD, silicon oxide or silicon nitride materials are deposited on all exposed surfaces of the CVD deposition chamber, as well as on the substrate. Typically, when such residues accumulate to a thickness of about 0.5 to 10 microns, the residues must be removed from the chamber surfaces prior to subsequent deposition processes. Otherwise, the residue material may flake from chamber surfaces, and may deposit on a substrate, compromising the integrity of features formed thereon.
Conventionally, deposition chambers are cleaned to remove residue using a plasma and select chemical compounds which react with the residue and form a volatile compound which can be exhausted from the chamber. Alternatively or additionally, the chemical compounds may form etching species which bombard the chamber surfaces to dislodge residue from the chamber components.
When a chamber cleaning operation is performed, semiconductor device production is interrupted and as a result, the effective productivity of the chamber, as measured by substrate throughput, decreases significantly. In order to increase chamber productivity, it is necessary to minimize cleaning operation time and to restart device production immediately thereafter. Therefore, it is imperative to determine precisely the endpoint of the cleaning process.
Because the time required for processing and cleaning determines production capabilities, semiconductor device manufacturers carefully monitor processing time relative to cleaning time. Accordingly, there is a need for an accurate and consistent determination of the endpoint of a process (whether a production process or a cleaning process). Preferably, the determination should be made using existing hardware and monitors.
The invention generally provides a method and apparatus for detecting the endpoint of a process by monitoring the position of a valve during the process. The inventive method allows endpoint detection for any process that requires throttle valve position changes in order to maintain chamber pressure within a desired range, and is particularly well suited for detecting the endpoint of a chamber cleaning process.
For instance, a remote microwave chamber cleaning process""s optimal chamber pressure is typically about 1.5 Torr. As chamber surfaces are cleaned via vaporization (e.g., etchant induced desorption) of material deposited thereon, the chamber""s throttle valve opens so that the vaporized material does not increase chamber pressure. As the cleaning process progresses less material vaporizes, the throttle valve position changes less, and eventually the throttle valve reaches a final constant position indicative of a clean chamber.
Each process has a unique pattern of throttle valve positions. Accordingly, to obtain a calibration signal the inventive method monitors throttle valve position while a given process is performed within a specific chamber to obtain a calibration signal for that chamber and for the given process (e.g., to obtain a calibration signal for a wafer processing process such as an etching process or a chamber processing process such as a cleaning process). A production instance of the process is then performed within the specific chamber, and the calibration signal is used to estimate the endpoint of the production process. The endpoint of the production process may be estimated by:
(1) equating the time at which the calibration signal indicates endpoint (i.e., the endpoint time (t)) with the endpoint of the production process; or
(2) filtering the calibration signal, monitoring the production process"" throttle valve position to obtain a production signal, filtering the production signal and comparing the features of the filtered production signal with the features of the filtered calibration signal.
Both the calibration signal and the production signal may be filtered by first determining a slope for each measured throttle valve position, and by then filtering the determined slopes (e.g., via a finite response filter). Thereafter, features may be identified by determining the sign (i.e., positive, negative or zero) of each filtered slope, by determining the duration of consecutive filtered slopes of like sign, and by defining a minimum duration of consecutive filtered slopes of like sign to identify features (e.g., five or more consecutive positive filtered slopes equals a positive feature).
The endpoint of the production process may be estimated, for example, to occur when the number, order and sign of the filtered productions signal""s features equal the number, order and sign of the filtered calibration signal""s features. When endpoint is estimated by either the first or the second method, it may be desirable to continue production processing for a period of time beyond the estimated endpoint time (i.e., for a total production processing time of t+N), to ensure that the endpoint has been reached.
An inventive computer program product for performing the endpoint detection process comprises a computer readable medium having means for storing a calibration signal comprising throttle valve positions for a given process (i.e., a throttle valve position calibration signal or a xe2x80x9ccalibration signalxe2x80x9d), and means for directing a controller to end a production instance of the process based on the calibration signal. The inventive program also may include means for monitoring the position of a throttle valve during performance of the production instance of the process (e.g., to generate a throttle valve position production signal or a xe2x80x9cproduction signalxe2x80x9d), means for filtering the calibration signal and the production signal, means for identifying features of the filtered calibration signal and of the filtered production signal, and means for comparing filtered production signal features with filtered calibration signal features to estimate the endpoint of the production process. Preferably the production signal is filtered via use of a low pass filter, most preferably via use of a low pass finite impulse response filter of order three.
With use of the inventive method and apparatus, processing endpoints may be determined with no additional hardware cost. Existing hardware may be used to monitor throttle valve position, to terminate a process and to store data and perform computations thereon. Further, the inventive endpoint detection method can be performed in real time, such that a process can be terminated precisely at its endpoint. Chamber productivity therefore is maximized.